Localizer antenna system



June 22, 1954 A. ALFORD 2,682,050

LOCALIZER ANTENNA SYSTEM Filed Feb. 5, 1951 3 Sheets-Sheet l INVENTOR.

Andrew 47 MW rimf A. ALFORD LOCALIZER ANTENNA SYSTEM June 22, 1954 3Sheets-Sheet 2 Filed Feb. 5, 1951 INVENTOR. And fllf q BY A;

Ili Mm Patented June 22, 1954 UNITED STATES F TENT OFFICE LOCALIZERANTENNA SYSTEM Andrew Alford, Cambridge, Mass. Application February 5,1951, Serial Nd. 209,431

13 Claims. (01. 343-407) The present invention relates to a combinationantenna array and more particularly to a localizer antenna system. Inthe present invention, the antenna. system comprises two arrays, a mainarray and a subsidiary array. The main array is intended to produce theprincipal localizer course as for instance along a landing'runway for anaircraft. The subsidiary array essentially provides the back course butbothof these elements cooperate with one another to effect and establisha complete localizer system.

Both arrays are essentially unidirectional, although the: subsidiaryarray which provides the back course sends out a substantial signal atright angles to the course. are operating, there is a signal in alldirections so that the aircraft approaching from a distance in anydirection will be able to pick this signalup and use it as a landingguide. The subsidiary array is energized with a carrier frequency whichis between and 'kilocyc1es higher or lower than the frequency of thecarrier used to energize the main array. Butxthe same modulation is usedonboth arrays so that the-signals received bythe aircraft receiver afterdemodulation are identical whether they come from'the'rnain array or thesubsidiary array and in fact the listener or observer willnot knowwhether the main'or the subsidiary array is responsible for the .signal. For instance, if the main array has a car'- rier frequency of 110megacycl'es and the sub sidiary-array: is energized 5 to 20 kilocycleshigher or lower than that frequency" then the frequency of thesubsidiary array would be 110.005 to 110K020 megacyc1es'or'109.080to1091995 mega cycles. The modulating frequency will be an audiofrequency of perhaps QO'cycles for the right antenna of the system and150 cycles for the left antenna of the system.

The fact that the carrier utilized in the two arrays are of diiferentfrequencies results in two benefits; (A) The interference in theoverlapped regior rbetween the'patterns of the main and of thesubsidiary arrayis avoided. (Bl Reflections frm obiiects in=the field ofthe subsidiary array cannot produce an interference pattern along themain course, so that sharp bends in the main course resulting fromobjects outside the radiation-pattern of the main array are avoided. Totake fulladvantage of this arrangement, it is desirablethat the mainarray be desi nated in such a way that its overall radiation patternwould occupy as narrow a, section as possible; The narrowerthis sectoris, the less chance thereis that there will be-a hangar; telephonewires; or

When both arrays other reflecting objects which could produce aninterference pattern and, therefore bend along the main course.

The present invention does not relate to the receiving circuits otherthanthe antenna system nor to methods of providing indications and anysuitable standard arrangement which are now known and employedmay beused for this system.

It will be seen from the specification as set forth below that the mainarray comprisespreferably two narrow beams producing a left beam and aright beam which will be energized with the same audio frequencymodulation corresponding to the left and right lobe of the subsidiaryarray so that'a resultant composite-signal may be received in thereceivers on the aircraft and may be used to produce an indication on ameter showing that the aircraft is on the right-side of the beam, theleft side of the-beam, or right on the beam. The virtue of thiscombination is that no matter-in what-direction the aircraft isapproaching the landing strip and no matter where the aircraft is, aslong as it is within the range of the subsidiary array, that a positiveand definite indication will be given to the aircraft. Without thiscombination, it is possible for'the aircraft to miss the beam entirely,particularly if the beam is very narrow,'since the aircraft may passthrough the beam before the observer has an opportunity to notice thathe is in the beam.

Without further describing the merits and advantages of the presentinvention, the invention will be described in connection with thedrawings illustrating an embodiment thereof in which:

Figure 1 shows somewhat schematically a general layout of the wholesystem.

Figure 2 shows a localizer radiation pattern of the'main and subsidiaryarray.

Figure 3 represents a so-called dumbbell pattern.

Figure 4 represents a calculated cloverleaf pattern of the radiation ofthe same antennas used in producing the pattern of Figure 3.

Figure 5 represents a calculated pattern of the radiation of the outerelements of the array of Figure 1.

Figure 6 represents a calculated pattern of the radiation of the centralpair and the next adjacent pair of antennas of Figure 1.

Figure 7 represents a calculated total c1over leaf pattern of theradiation of the array of Figure 1.

' Figure 8 represents a calculated localizer pattern combining bothcloverleaf and dumbbell patterns of the array of Figure l; and

Figure 9 shows a full wave dipole which may be used as the end arrayelement of the structure of Figure 1.

In the arrangement shown in Figure 1, the main array comprises elementsI, 2, 3, 4, 5, and 6 arranged in a straight line at right angles to theprojected course with each element being used for producing both leftand right beams of the type illustrated in the composite pattern ofFigure 8. Antenna elements 3 and 4 are each ap proximately half wavedipole and so also elements 2 and elements 3 and 4 forming one pair andelements 2 and 5 forming a second pair. Elements l andrfi are onewavelength'long and may be constructed as shown in the structure ofFigure 9. Each of the elements may be provided with correspondingreflectors I, 2", 3', 6', 5, and 6 with the antenna units all on thesame side of the reflectors. The central pair of units 3 and d are fedby a coaxial bridge '5 which preferably is of a type described in myapplication, Serial No. 175,694, filed July 25, 1950. The units 2 and 5are fed in opposite phase through a transformer 8. The full wave- 4through the coaxial bridge by means of the transmission line 5 andenergized in opposite phase. The calculated patterns for the combinationof antennas 2 and 5 which are also fed in opposite phase is somewhatlike the arrangement of Figure 4: except that the radiation lobes may besomewhat narrower and two auxiliary lobes are present, symmetricallypositioned at a greater angle from the line of the course than the twomain lobes.

A calculated pattern of the radiation of ele- 'ments I and 6 whenenergized in opposite phases is shown in Figure 5. This calculatedpattern shows that there are 2 sets of auxiliary lobes on on the outersides of the pair of main lobes and that .inthiswcase the main andauxiliary lobes tend to be narrower than in the case of the com- Ibination of elements 2 and 5.

length antennas I and ii are also fed through v the transformer 8 inopposite phase and the coaxial bridge I is also fed from the transformerby means of the transmission line 9. It will be noted in the arrangementof Figure 1 that the antennas I, 2 and 3 are energized in the same phaseand 2, 5 and 6 are also energized in the same phase which is opposite,however, to the phase of energization of the antennas I, 2 and 3 so thaton each half of the course the antennas are fed in the same phase butOpposite to the antennas on the other half of the course. This appliesto the so-called cloverleaf energization of the antennas. Thetransmission line 9 which impresses its energy into the coaxial bridgeat its lower end has a balanced output by means of this feed through thearms l8 and i I which are in the same phase so that the feed from thearms I0 and II to the antennas 3 and i respectively are connected inreverse phase as indicated by the connecting elements I2 and I3respectively. The construction of the coaxial bridge of the applicant asshown in his copending application also indicates that when the coaxialbridge 1 is fed by the transmission line H! into the top end of thecoaxial bridge, the outputs in the arms It and II are in opposite phaseso that by effecting connections 52 and It as shown the result is thatthe energy fed by means of the line It will be in phase in the antennastructures 3 and d. The'transmission line feed it in the present systemhas been given the name dumb-bell feed while the feed by thetransmission line 9 is given the name Cloverleaf feed. The patternresulting from the combination of 3 and i when the energy is in the samephase results in a single lobe symmetrical with the line of the course,whereas when the energy in the antennas 3 and 4 are in opposite phase,two lobes are provided which together should form a symmetrical patternwith the line of the course.

Figure 3 shows a calculated dumb-bell pattern, that is, a patternobtained by antennas 3 and 4 when fed through the coaxial bridge bymeans of the transmission line M so that antennas 3 and 4 are energizedin the same phase.

Figure 4 shows a calculated pattern of radiation of the same antennas 3and t when fed 'The' combined calculated pattern of elements 2, 3, 4 and5 shown in Figure 6 provides a cloverleaf pattern of two lobessymmetrical with the line of the course, each lobe being narrower ormore directive than the calculated pattern for the center pairpreviously described.

The total pattern combining all'of the six elements except the in-phaseradiation of elements 3 and 13 obtained through the coaxial bridge I,

by energization over the transmission line I4 is shown in Figure 7, thepurpose of the combination being to emphasize the main lobes and reducethe auxiliary lobes. .The ultimate result which is the combination ofenergization through the cloverleaf and dumb-bell patterns is shown inFigure 8 and indicates that the left main lobe and the right main lobeoverlap in a symmetrical center region directed along the axis of thecourse and subtending a comparatively narrow angle. It should be notedthat each of the full wave end radiators are considered the equivalentof two half-wave radiators.

This resultant main array produces a difierent signal on one side of thecourse from that on the other so that when the aircraft, for instance,or whatever device which may have the listening apparatus is observed,the beam patterns will provide a balance when on course and left orright signals'when to the left or right of the course respectively. Themeans for providing this indication itself may be any of the usualapparatus used for this purpose and does not in itself form a part ofthe present invention.

The radiation elements I to 6 produce the main array. The subsidiaryarray is produced by the two radiating members I5 and I6 which are alsosymmetrically positioned with respect to the line of the course. Theseradiators I5 and I6 may be cylindrical or oval in cross section with airgaps I? and I8 respectively symmetrically positioned on one side of theshell parallel to the axes thereof. The radiators I5 and i5 comprisingthe subsidiary array will be energized from a high frequency source I9whose frequency will be between 5 to 20 kilocycles higher or lower thanthe frequency of the carrier source 20 used to'energize the bridgecircuit 2! for the main array. The subsidiary array comprising theradiators I5 and I6 will be modulated preferably by an audio frequencysource. This may be accomplished mechanically by the motor 22 providedat each end with shaft extensions 23 and 24 carrying disks 25 and 26which are provided with uniformly spaced teeth which rotate in a planebetween the difierent sides of the transmission lines 21 and 28. If thedisk 25 is provided with three teeth and the disk 26 with five teeth,then the moduaesagoro:

oftthe: radiator Hi, 159 cycles-pervseoondzcl.The:

motor- :22; and; the: motors!) for the main zarray;are'drivenezsynchronously oronermotoremayeserve to rdriveithe shafts2-3523f2l1l1173h'32 so thatithe diskslflsand al -which are :similarrespectively to therdisksafizandifisfitwilliprovidecthersame modulation; iorethe; left and; rightrisidetofsthe array: system. The coaxialtransmission; abridge 211 changes :the phasewof 1energyrfedithrough"the: branchirtw to be opposite from that. fed:through; therbranc'h 4| sothatif the carrier is modulated by 90 cyclesby the zdisk.-33;: thetenergy-atlniouglr therbranch: 4!] will nc'omeiout-in opposite phasei'to that onfthe energy in thei'branchf lL:.,Therenergyt through the branches r42 and lfi will, howeve'nbe in thesamecphase, and-in phase with the: energy: fed" through branch. 4 I .1The. energynf each outletofthetransmissionzbridge 21 goes. through thebaiuns35 and 36 respectively ltorthe transformer 8 and? to thetransmission-:-'line l4 respectively; The balunsareessentially abalancing element: usedrgener'ally in ;:the. art; forv a description ofwhich reference is had to an article in VeryrI-Iigh': FrequencyTechnique? vol; 1, Chapter 3, by Radio Research" Laboratory. Staff;'published' by Mo:- Graw-Hill, 1 947: x

Since-:the power :deliveredto the 1 cloverle'af should bee-aboutone-quarter of the power de-= livered to the dumb-bell, an. adjustable:attenuator 31 is providedtbetween the:balun 35 and the transformer "8.This'zattenuator is adjustedto obtain a balancebetweenthe fdumbebell andcloverleaf DHZCIGGIIIS'ISO' that Itheeultimate pattern produced:willzbeislibstantially' asashown "in Figure 8:

Figure ,2 which shows a composite'pattern of the: main andrsubsidiaryarraysis 'shown as -hav ing two-main lobes. A and. B, the: left lobevAlying mestly to the-leftof the course linec andr-the lobe B to the right'of the course line: rThensignalgivenebym-the -left l-obeaAwillxcorrespondito the 4 modulation-of themodulating. element 33 Which;may be 90- cycles per second; while the modula=a tion corresponding tothe 'rightlobe B will be: #150 cycles per second, because of themodulatingiele merit-:24. Thisnapplies also for the-dotted mainsubsidiary lobes D and E, respectively; the :lobe D having :a modulatingfrequency corresponding to the modulating element 25 Ethe lobe E has amodulating frequency corresponding to the modulating element 26. Alongthe course line C,

thei'stwo signals are balanced and, "therefore," a balancedmdicator-"mayv-be"used to indicate that the pilot is on this course. Ifthe pilotshould deviate to the left of the course, the signal fromthe'-lobe A wiltprevail, while if The deviates-to therightof' thecourse; the signal on the lobeB willprevail:

Thesubsidiary'array in the present invention is intended to provide aback course in which this array sends out a substantial signal at rightangles to the course. This will be evident from the lobes D and E inFigure 2 from which it will be seen that the subsidiary array isintended to cover directions other than those in which two main lobesare situated. Since, however, the modulation of the subsidiary array andthe main array lobes correspond, the operator will not realize that heis listening or observing one or the other of these lobes. Thesubsidiary array is far less strong in the forward direction of the inFigure 9:

6 beams n :amtsB than sth'erit-beamswn andz Bso' thatatheelsubsidiaryarrayzawilllnot ..-be':-. dominant inithesessections;

The factors? controlling the deviation of. the:beamsifromthecentra1-courselineare first that theitradiators on the."right and the left side -of the" oenter'are fed inopposite phases andsecondly that while the dumb-bell is fed with modulated carriersrin additive'phaseythe fcloverleaf is fed 5with'zonexmodulatedcarrienin:oppositezphase to that of the othermodulated carrier throughthe: transformer 8-. 1 The'resultingpatterny-therefore, asexplained in Eigurefl is obtained:

The radiators 2, 3, 4 and S are preferablybal anced slot fed dipoles ofhalf wave lengthven' ergized through: the coaxial transmission linesextendingthroughzthestem of the T as indicated diagrammatically inFigure l.

The end radiators are azfull wave length and a full section ofrthefstructure 'for: thesev radiators is shown in Figure:9. Thisstructure is essentially an aarray'of two 1 half wave length. elementsplaced-:nexttoeachnther. The-feeding arrange-- ment, however, is simplerthan that-for'a halt; wave-element;

The outer conductors of thetwo half waveele--- ments consist of two Ts51 rand -52- which in sectionimay-belzcylindrical, ovalor other type:vof section: commonly "usedv 1 as a "coaxial "transmission H-line. Here#the :conductor designated as ey lindrical-is intended :toi'inclu-de--other types :of

sectionssas'well. The full-wave element is fed: through thewstemofone T.i This comprises the outer conductive cylinder-.53 and the inner:cylinder 54 forming'a coaxial transmission line. The:

inner cylinder 54 is spacedv-and insulated from. the outer cylinder "andis' connected :at top: to-

the inner conductor '56 concentrically positioned within the righthaltof the: outercrossbar'55" by the conductive-strapS-l. Theinnerconductor 56; is :insula'tedvby; suitable insulator disks fromtherouter=-conducton55 and connects through ins:

sulating .end :cap .58 :to the cap 62 *of the crossbar of the:outer-conductor 63 :Of the;

conductive connection tromthe terminal-=60 to the terminal-6|" of theconductive cap 62, atrthe inneraend ofcthe cylinder 63 which forms-the:

cross barfor the T 52:

In -a constructionnzwh-ich. I have successfully: used; the impedancebetween the ends of i the: Ts was approximately. 650 ohms matche'drtoa52.5-ohm line byatransformer having a Zn of 184- 011-1115;

The :designs: of :t-he full wave' element is 'such that .thereare smallcurrents flowing along the stems: of both Ts. These-currents fiowriniopposite directions in the two stems: At first it wasbelievedthat-=this-might:result in excessiveradiation-torvperhapsfevenein minorloads in the cures:tion.atu'ight'anglestofthefstemszs The only effect of 1 the stemrcurrentscis to tbroadenslightlythe T at;=the: right A conductiye'strap259 *makes 'a good.

7 nitude of radiation in the direction of the beams than the beamradiations, the beam and the broad lobe radiation on one side of the.course having the same modulating frequency and the beam and broad loberadiations on the other side of the course also having the samemodulation frequency but differing from the firstmodulation frequency.

2. A system as set forth in claim 1 in which the modulating frequenciesare in the low audible range.

1 3. A system as set forth in clainrl in which the modulating frequencyof 'one group is in the vicinity of 90 cycles and the other in thevicinity of 'l50 cycles.

4. A- system as set forth in claim 1 in which the beam patterns aredirected generally slightly to the left and right of the courserespectively and the otherradiation lobes are mainly to the sides andrear of the beam patterns. I

5. A system as set forth in claim 1 in which the broad lobes have acarrier-which is'in the range from 5 to 20 kilocycles higher or lowerthan the main carrier.

6. A localizer signaling system for'g'uiding a craft along a coursecomprising a main array for producing a pair of intersecting lobes onedirected to the right and the other to the left of the course and asubsidiary array for producing'lobes to the right and left of the courseof lower intensity than the beams, means energizing the elements of thearrays to the right of the middle of the array in opposing carrier phasefor that of the elements to the left of the middle, means for modulatingthe carrier of the main array with two different low frequencies inopposing phase and the pair of main array elements'adjacent the middlewith the two different low frequencies in the same phase.

' '7. A system asset forth'in claim 6 in which the pair of main arrayelements adjacent the middle are energized with the two different lowfrequencies in the same phase at approximately four times the power asthe energization of the main array elements in opposing phase.

- 8. In' a localizer'system of the type described, a main array having aplurality of radiators substantially at right angles tothe intendedcourse, a coaxial bridge element energized simultaneously at both endshaving opposing side outlets connected to the middle positioned elementsof the array, said coaxial bridge element having means for reversinginphase the energy fed to one end from that of the energy fed to the otherend and means for feeding the other elements of the array through atransmission line having the same phase as the energy fed to one end ofsaid coaxial bridge.

9. In a localizer system of the type described, a main array having aplurality of radiators substantially at right angles to the intendedcourse, a coaxial bridge element having two input ends and two outputends with means containedaesaoao.

therein for reversing the phase of the outputs .fed' from one input endfrom that fed from the other input end, feed lines connectedfrom saidoutputs to the middle positioned array elements, a balanced transmissionbridge, a transformer;

energizing means for energizing said transmission bridge and stillfurther feed lines connecting from the output of said transformerdirectly to the other elements of said array.

10. A system as set forth in claim 9 inwhich the energyfed through thetransformerhas approximately one fourth of the power as the energy feddirectly. to the coaxial bridge. .11. A system as set forthin' claim 9in which means are provided between the balanced trans mission bridgeand the transformer for attenu-' ating' the power passing therethroughto approximately one'fourth that fed directly from the balancedtransmission bridge to the coaxial bridge.

12. A system as set forth in' claim 9 in which the means for, energizingsaid transmission bridge includes means for low frequency audio 'modula'tion of the carrier wavewith two diiferent frequencies each in differentfeed lines to different sides-of the transmission bridge, saidtransmission bridge having one arm effecting a reversal of phase ofpower passed therethrough;

' 13. A localizer signalingsystem for guiding a craft along a coursecomprising a group of antennae forminga main array and a group ofantennae forming subsidiary array, means energizing individual antennaeof said main array to produce dumb-bell and cloverleaf radiationpatterns respectively, and to form together a pair of main compositebeams directed to the left and right of the course respectively butover-' lapping narrowly along the course, means for producing with saidsubsidiary array radiation patterns of substantially rounded lobes tothe right and left of the course and intersecting narrowly on the courseof substantially less intensity than the beams of the main array andmeans for modulating said arrays with different audio frequencies forthe right and left lobes respectively-whereby the direction of thecourse may be established.

1 References Cited in the file of this patent V UNITED STATES PATENTSNumber Name Date 2,212,238 Kolster Aug. 20, 1940 2,283,677 KandoianMayl9, 1942 232L454 Brown June 8, 1943 2,402,3'78

Davies fl l June 18, 1946

